Paperboard is used every day to create products such as disposable picnic supplies, covers for paperback books, folding cartons and beverage carriers. In the paper industry, the term paperboard refers to heavy papers like board stock. Board stock is a subgroup of paperboard used to make paper cups and plates, hot and cold food containers, ice cream containers, paper back book covers and the like. Box board, a second subgroup of paperboard, is used to make folding cartons such as cereal boxes, beverage carriers, and tissue boxes.
The end use of a product made from paperboard dictates the type of paperboard used. Paperboard characteristics such as cushion, strength, stiffness, wear resistance, coefficient of friction, density, caliper, color, brightness and smoothness are generally considered. In applications where enhanced printed graphics on the product is critical, characteristics such as smoothness and brightness are most important.
Typically, when smoothness and brightness are the desired paperboard characteristics, a solid white paperboard is used. This white paperboard, commonly referred to as Solid Bleached Sulfate, is produced from bleached pulp and used for many of the aforementioned purposes. Though bleached paperboard characteristics contribute to improved printed images, it is considerably more costly to produce and lacks the strength of an unbleached paperboard, and does not provide an ideal surface on which to print high quality graphics.
Other paperboards are even less desirable for printing high quality graphics than Solid Bleached Sulfate paperboard. For instance, unbleached boards have surfaces that are relatively rough or uneven. Unless certain manufacturing processes like clay coating the paper surface or bleaching the pulp are employed, the paperboard surface normally has a gray or brown color. Printing directly on a dark color of the unbleached board provides poor visual contrast for the printed image. Thus, folding cartons used for protecting cosmetics, luxury items, or paperback covers often display a very high quality graphic image that requires use of a higher quality paperboard than has been bleached and/or clay coated.
The prior art discloses a laminated package used for beverage carriers. The prior art discloses a sheet or web of clay-coated or other publication paper that is printed with graphics and stored for subsequent application to a cellulosic substrate. The cellulosic substrate generally consists of one or more plies of unbleached virgin kraft pulp. At the paperboard converting manufacturing site, the coil printed paper is unwound and bonded to a surface of the moving cellulosic substrate with an adhesive to provide a laminated material used to make packages. However, since the thin layer of paper is relatively translucent, the dark colored cellulosic substrate may show through the printed paper and detracted from the appearance of the graphics. To prevent “show-through”, finely divided particles of generally inert white pigment, such as calcium carbonate or titanium dioxide are incorporated in the adhesive, or alternatively, a second clay coat is applied to the undersurface of the paper prior to bonding the paper to the substrate.